1. Field of the Invention
The present invention relates to a process of preparing oil out of vegetable material or oil bearing seeds, such as cottonseed, rapeseed, safflower seed, sunflower seed, linseed and the like, and particularly, to a process including the combined steps of mechanically expelling oil from the seeds and chemically extracting the remaining oil from the expelled pulp or cakes by a solvent.
2. Description of the Prior Art
Referring to FIG. 1, a conventional prior art process of extracting oil out of vegetable material, such as cottonseed, rapeseed, safflower seed, sunflower seed, linseed and the like, includes both a mechanical expelling step and a chemical solvent extraction step. The oil bearing vegetable material, which is pre-treated by cleaning and cooking, is first fed into an expeller 1. A typical expeller of the continuous press type, illustrated in FIG. 4, has a truncated Archimedes screw blade 14 rotated within a mating truncated housing 15 which converges from an inlet 16 thereof to an outlet 17 thereof. The housing 15 has a large number of openings or pores in the bottom thereof opening up into a crude oil collection chamber 18. The cleaned and cooked material inserted into the inlet 16 is compressed and crushed as the material is propelled from the inlet 16 to the outlet 17 by the screw blade 14 and housing 15 to mechanically expell a large portion of crude oil from the material through the openings in the housing into the chamber 18 while the compressed cakes or pulp, still containing a large quantity of oil, is propelled out of the exit end 17 of the expeller. The mechanically expelled oil within the chamber 18 contains sediments and particles of various sizes which must be removed to produce an oil of suitable quality.
The mechanically expelled oil from the expeller 1, FIG. 1, is sequentially (a) passed to a screen tank 6 where sediments of relatively large size are separated from the crude oil, (b) transferred by a pump 7 from the tank 6 to a decanter 8 where fine sediments or sediments of relatively small size are removed, (c) transferred by a pump 9 from the decanter 8 to a tank 10 wherein the crude oil is heated to a temperature of 100.degree. C to reduce the viscosity of the crude oil, and (d) fed by a pump 11 from the tank 10 to a filter press 12 wherein very fine sediments are separated from the oil. In the case of cottonseed oil, the heating step in the tank 10 is eliminated to prevent tinting by heating. A typical filter press of a flush plate frame type, illustrated in FIG. 3, has alternately located plates 20 and frames 21 with screening fabric 22 held between the plates 20 and frames 21. The liquid to be filtered is fed through an inlet 23 into the frames 21 to pass through the filtering fabric 22 into the plates 20 from which the filtered output, having all the sediment removed, is collected.
The compressed cakes discharged from the expeller 1 are broken into small pieces by a crushing roller 2 and then fed into a chemical extractor 3 wherein a suitable solvent is flowed through the cakes to extract the oil from the cakes. Miscella, the mixture of crude oil and solvent, from the extractor 3 is collected in a miscella tank 4 and then fed into a distiller 5 where the solvent is separated from the oil.
The decanters, filter presses, oil heating means, and various other pipings and accessories therefor, involve a considerable initial expense and subsequent maintenance and operation. Fabric filtering elements for filtering fine sediments must be cleaned periodically and such cleaning is often difficult. Also the heating of the crude oil required fro reducing the viscosity of the crude oil for filtering by the filter press 12 can deteriorate the quality of the edible oil; i.e. the crude oil when heated in contact with air can become tinted to an extent that it cannot be de-colored during subsequent de-coloring steps, and/or it is deteriorated or impaired in its flavor. Also finished oil products, particularly cottonseed oil, subjected to heating steps during the preparation process have a tendency to become tinted later during storage.